A composite object is typically formed from two or more materials to obtain an advantage from the combined properties of those materials. For example, it is common to fabricate an object such as a bicycle frame from carbon fibre, which is a composite material, as a composite bicycle frame has a beneficial weight to stiffness ratio.
Additive manufacturing, commonly known as 3D printing, is a manufacturing technique used to fabricate objects. An additive manufacturing process typically involves preparing a digital 3D model of the object with computer software, deriving computer instructions from the 3D model which define a series of parallel, planar cross-sections of the object geometry and providing a 3D printer with the computer instructions, which guide the 3D printer to fabricate successive layers of material corresponding with the cross-sections, one on top of another, until all of the object layers are fabricated.
Many different types of additive manufacturing processes exist, the most common being stereolithography (SLA), selective laser sintering (SLS) and fused filament fabrication (FFF). Stereolithography involves tracing the cross-sections of the object on a top surface of a vat of liquid curable photopolymer with a light source (typically being an ultraviolet laser or lamp), causing the liquid photopolymer to cure to a consistent depth where the light source is focused on the top surface. The cured photopolymer forms a layer of the object and is supported on a platform arranged in the vat. After the layer is fabricated, the platform is lowered into the vat by the thickness of the layer, and a second cross-section is traced, forming a second layer which bonds to the first layer. This process is repeated, with successive layers being fabricated and the platform progressively lowering into the vat until the object is fabricated.
Stereolithography offers a number of advantages over traditional manufacturing techniques, such as injection moulding. However, stereolithography, also suffers from a number of drawbacks. For example, there are many occasions where it would be useful to fabricate an object from a composite material, having specific physical characteristics such as increased strength or reduced density, using stereolithogaphy. Past attempts to resolve this have involved adding fillers, such as ceramic or metal particles, to the liquid photopolymer to form a curable suspension which when cured, fabricates a composite object. However, as the curable suspension is largely homogenous, the resulting fabricated composite object has consistent material characteristics throughout the entire part and therefore does not allow specific portions of the composite object to be fabricated having specific, desired properties.
Accordingly, it would be useful to provide a method or apparatus for selectively solidifying liquid curable material which allows a composite object to be fabricated from two or more materials which has different portions having different material properties.